1. Field of the Invention
The present invention relates to a construction of an ink jet print head that can be installed in an ink jet printing apparatus and also to a method of manufacturing the same. More specifically, the invention relates to a method of bonding together with high precision in a short period of time a printing element substrate formed with ink ejecting print elements and a supporting member for supporting the printing element substrate and supplying it with ink.
2. Description of the Related Art
The ink jet printing apparatus uses a print head having a plurality of printing elements that eject ink according to print data to form dots and therefore an image on a print medium. In recent years, great efforts are being made to develop a print head capable of ejecting smaller ink droplets at high density to print highly defined images with enhanced precision.
FIG. 9 is an exploded perspective view of a side shooter type ink jet print head disclosed in Japanese Patent Laid-Open No. 2006-015733. The ink jet print head 1 has a printing element substrate 110 with a plurality of printing elements, a supporting member 120 to supply ink to the printing element substrate 110 and an electric wiring board 130 to transmit a print signal to the printing element substrate 110.
FIG. 10 is a perspective view showing the construction of the partly cut-away printing element substrate 110. The printing element substrate 110 has a silicon substrate 111, about 0.5-1 mm thick, formed with a groove-like ink supply port 112 by an anisotropic etching based on silicon crystal orientation or by sand blasting. On both sides of the ink supply port 112 on the silicon substrate 111 there are arranged electrothermal transducing elements 113 at a pitch corresponding to the print resolution. These elements 113, along with aluminum electric wiring for supplying electricity to the elements 113, are formed by photolithography. On the silicon substrate 111 an ink path-formed member 118 having ink paths 116 to introduce supplied ink to ejection openings 117 is arranged so that the ejection openings 117 face the electrothermal transducing elements 113. Each of the printing elements comprises the electrothermal transducing element 113, the ink path 116 and the ejection opening 117. The ink introduced from the ink supply port 112 to the ink paths 116 is ejected from the ejection openings 117 as ink droplets by a bubble expansion energy produced by individual electrothermal transducing elements 113. As the printing operation proceeds, ink is supplied stably from an ink tank on a supporting member 120 connected to the printing element substrate 110.
The supporting member 120 is designed not only to supply ink to the printing element substrate 110 as described above but also to support the printing element substrate 110 at a predetermined position. It is therefore desired that the supporting member 120 and the printing element substrate 110 be put at the predetermined relative positions in horizontal and vertical directions with high precision. More specifically, first, the ink supply port 112 of the printing element substrate 110 needs to be placed precisely at the position of an ink supply path formed in the supporting member 120. It is also desired that the direction in which the plurality of printing elements are arrayed in the printing element substrate 110 be set perpendicular to the main scan direction of the print head 1. Further, the ejection opening face of the printing element substrate 110 needs to be set parallel to a support surface 121 of the supporting member 120. Unless this third condition is met, the ejection opening face may be inclined with respect to a print medium, causing the ejected ink droplets to land on the print medium at an angle, degrading printed images.
The supporting member 120, however, is generally a molded product for reduced cost and improved processability, so that its support surface 121 may often result in a complex three-dimensional geometry, failing to have an ideal smooth surface. If the printing element substrate 110 is bonded to the unsmooth support surface 121 as is, the ejection opening face of the printing element substrate 110 can be directly affected by the three-dimensional slight undulations of the supporting member 120, being difficult for securing a plane parallel to the print medium.
For example, Japanese Patent Laid-Open No. 11-147314 (1999) discloses a construction in which a plurality of raised flat portions are provided on the support surface 121 and their flatness is kept in good condition to improve the parallelism of the ejection opening face. With this construction, if the support surface 121 other than the raised flat portions includes three-dimensional undulations, the horizontal plane of the ejection opening face can be secured.
Another technique has also been available in recent years in which the printing element substrate 110 is kept precisely at the predetermined position horizontally and vertically with respect to the support surface 121 by using CCD camera or the like and a bonding adhesive filled between the printing element substrate 110 and the support surface 121 is hardened by ultraviolet light.
FIG. 11 shows a process of assembling the print head that employs the above-described methods. First, in step 1, the support surface 121 of the supporting member 120 is applied with a thermosetting adhesive 125. Next, in step 2, the printing element substrate 110 electrically connected to the electric wiring board by a gang bonding method is sucked by a supply finger 600 and moved to over the supporting member 120. Further, in step 2, by using an image processing system with two CCD cameras, the printing element substrate 110 is located precisely at the predetermined position horizontally and vertically.
In step 3, the printing element substrate 110 is lowered to engage the thermosetting adhesive 125. At this time, the printing element substrate 110 is loosely placed in or floating on the thermosetting adhesive 125 without contacting the support member 120. Then, in step 4, with its attitude held as is, the printing element substrate 110 is heated by ultraviolet rays emitted from a light application device 620. This causes the thermosetting adhesive 125 in contact with the printing element substrate 110 to gradually harden, firmly bonding the printing element substrate 110 and the supporting member 120 together. Finally, circumferential portions of the printing element substrate 110 and its electric connections are sealed with a sealing material and heat-cured. Now, the print head is complete.
With this method, if there are slight undulations in the support surface 121, the adhesive layer with a uniform thickness greater than the height of the undulations enables the printing element substrate 110 to be bonded to the support surface 121 so that its ejection opening surface is horizontal. Such a method of bonding the printing element substrate using CCD and thermosetting adhesives is disclosed, for example, in Japanese Patent Laid-Open No. 2002-154209.
Even with the method of Japanese Patent Laid-Open No. 11-147314 (1999), however, there are some variations in height among a plurality of raised flat portions. The height variations make it difficult to achieve the degree of high levelness required in recent years. More specifically, although the height variations among the raised flat portions need to be kept within 10 μm from the standpoint of the print position accuracy, actual molding inevitably produces height variations of about 20 μm.
In the construction that uses an adhesive layer thicker than the height variations of undulations, the ejection opening surface of the printing element substrate 110 can be bonded parallelly to the support surface 121 without having to provide a plurality of raised flat portions. That is, although the support surface 121 of the molded part has undulations of about 50 μm, the use of the adhesive layer with a thickness of about 70 μm, greater than the undulations, enables the printing element substrate 110 to be fixed horizontally without being influenced by the undulations.
However, increasing the thickness of the adhesive layer naturally increases the amount of heat required to harden the thermosetting adhesive to a sufficient degree of hardness, i.e., the time it takes for the adhesive to harden. This in turn increases cost and time in the mass production of the ink jet print heads.